Apparatus for insulating thin electric conductors, particularly extremely thin copper conductors, with thermoplastic synthetic materials

ABSTRACT

Apparatus for insulating thin electric conductors, particularly extremely thin copper conductors, with thermoplastic synthetic material includes a tank for containing a thixotropic dispersion of the synthetic material, a coating roller mounted outside the tank and provided with a pair of spaced surfaces between which the conductor is to be passed in a vertical direction, and means for supplying the dispersion from the tank to the coating roller in an amount adequate for coating the electric conductor therewith, the coating roller being rotatable in a direction opposite to the direction in which the conductor is to be passed.

United States Patent [72] Inventor Bernhard Dinse 894,592 7/1908 Callan1l8/DIG. 20 Schwekertdam 322, 1 Berlin 13,Germany 1,031,620 7/1912callan 118/6 [211 App]. No. 745,763 2,269,150 1/1942 Flynn 118/234 X[22] Filed July 18,1968 2,649,758 8/1953 Cowgill 118/259 X [45] PatcntedJune 29, 1971 v rmary Exammer-John P. McIntosh [731 Ass'gnee if??? fBerh" and Attorneys-Curt M. Avery. Arthur E. Wilfond. Herbert L.

. umc ,erman Lerner and Daniel J. Tick [54] APPARATUS FOR INSULATINGTHIN ELECTRIC CONDUCTORS, PARTICULARLY EXTREMELY THIN COPPER CONDUCTORS,WITI-I RM PL STI YN BE AT A I 0 A c? T Em LS ABSTRACT: Apparatus forinsulating thin electric conduc- 1 Claim, 4 Drawing Figs.

tors, particularly extremely thm copper conductors, with ther- [52] US.Cl 118/67, moplastic synthetic material includes a tank f containing a 1l8/23 4, l 8/ thixotropic dispersion of the synthetic material, acoating It. Q roller mounted ouside the tank and provided a pair of ofSearch l spaced urfaces between the conducor is to be DIG v 259, in avertical direction, and means for supplying the dispersion R f cgtedfrom the tank to the coating roller in an amount adequate for l 1 eerences coating the electric conductor therewith, the coating rollerUNITED STATES PATENTS being rotatable in a direction opposite to thedirection in 246,728 9/1881 Crich et a1. 1 18/234 X which the conductoris to be passed.

PATENTEH JUN29 19?:

SHEET 1 OF 2 APPARATUS FOR INSULATING THIN ELECTRIC CONDUCTORS,PARTICULARLY EXTREMELY THIN COPPER CONDUCTORS, WITH THERMOPLASTICSYNTHETIC MATERIALS My invention relates to apparatus for insulatingthin electric conductors, particularly extremely thin copper conductors,with thermoplastic synthetic materials.

In the copending application Ser. No. 392,775 of H. Gerland et al.,filed Aug. 28, 1964, now U.S. Pat. No. 3,47 l ,327, and assigned to theassignee of the instant application, there is described a method ofinsulating thin electric conductors, particularly extremely thin copperconductors, with thermoplastic synthetic materials, preferably withpolyolefins, such as polyethylene especially. The viscosity of thepolyolefin is mechanically reduced at the locality where the conductoremerges from the dispersion. Thereafter, the dispersioncovered conductoris passed through one or more heated furnace zones wherein thedispersion medium is evaporated and the pulverulent polyolefin remainingon the conductor is sintcred to form a homogeneous coherent coating.

This method is employed primarily when the insulating layer to beapplied to the conductor is thin but must nevertheless be centered aboutthe conductor. By the method of the aforementioned copendingapplication, insulating walls are able to be applied to thin conductorssuch as copper conductors having a diameter of 0.3 mm. for example.Conventional extrusion presses are able to produce such thin walls forcentered copper conductors only with great difficulty and at great cost.

In the aforementioned copending application, apparatus has already beendescribed for carrying out the method disclosed therein, by means ofwhich the viscosity of the thixotropic dispersion is reduced by acoating roller having two opposed surfaces or flats between which theconductor being insulated is vertically traversed. In the embodiment ofthe apparatus disclosed in the aforementioned copending application,this coating roller is located within the tank containing thethixotropic dispersion. For this purpose, the tank is open at the top sothat the relatively large surface of the thixotropic dispersion is incontact with the air and, consequently, evaporation of the dispersionmedium occurs which, in turn, causes an undesired change in theviscosity of the dispersion.

It is accordingly an object of my invention to provide apparatus forinsulating thin electric conductors, particularly extremely thin copperconductors, with thermoplastic synthetic materials, which avoids theaforementioned disadvantages and difficulties of the aforementionedcopending application.

With the foregoing and other objects in view, in accordance with myinvention, I provide a coating roller that is located outside of thesupply tank proper of thixotropic dispersion and provide the roller witha pair of spaced surfaces between which the conductor is to be passed ina substantially vertical direction, and means for supplying an amount ofthe dispersion adequate for coating the conductor therewith from thetank to a location of the coating roller substantially diametri callyopposite the location thereof along which the conductor is to be passed,the coating roller being rotatable in a direction opposite to thedirection in which the conductor is to be passed. Assurance is therebyprovided that only a small part of the dispersion will come into contactwith air whereas the larger part of the dispersion will be enclosed inthe tank proper which is completely covered, so that undesiredevaporation of the dispersion medium is prevented. Since the viscosityof the thixotropic dispersion is reduced only at location where shearingforces occur, there forms on the traversing conductor a thin, centeredor coaxial coating having a thickness that can be determined in essenceby the rotary speed of the coating roller.

It is an important feature of my invention that the conductor to beinsulated does not have to first traverse the entire supply tank ofthixotropic dispersion but rather only the portion of the dispersionwherein the viscosity of the thixotropic dispersion has been reduced byshearing forces or shear stresses. Directly after the conductor leavesthe vicinity of the coating rollers, or directly after the conductor haspassed out of the dispersion supplied thereto by the coating roller, thedispersion surrounds the conductor homogeneously and concentrically orcoaxially due to the thixotropic characteristics thereof.

In accordance with yet another feature of my invention, I provide a pumpfor pumping thixotropic dispersion from the supply tank to the coatingroller.

In accordance with a further feature of my invention, I pro vide wipermeans adjacent the coating roller for adjusting the amount of dispersionsupplied to the coating roller and accordingly to the conductor that isbeing coated with insulation.

In accordance with a concomitant feature of the invention and in orderto adjust the thickness of the coating to be applied to the conductorwith accuracy, the coating roller is mounted so that it is adjustable ina direction substantially perpendicular to the substantially verticaldirection in which the conductor traverses the space between theopposing surfaces of the coating roller in a manner corresponding tothat described in the Austrian Pat. No. 259,048, in the name of theassignee of the instant application.

Other features which are considered as characteristic for the inventionare set forth in the appended claims.

Although the invention is illustrated and described herein as embodiedin apparatus for insulating thin electric conductors, particularlyextremely thin copper conductors, with thermoplastic syntheticmaterials, it is nevertheless not intended to be limited to the detailsshown, since various modifications and structural changes may be madetherein without departing from the spirit of the invention and withinthe scope and range ofequivalents of the claims.

The construction and method of operation of the invention, however,together with additional objects and advantages thereof will be bestunderstood from the following description of specific embodiments whenread in connection with the accompanying drawings, in which:

FIG. I is a diagrammatic view of apparatus for coating an electricconductor wire with thixotropic dispersion in accordance with myinvention;

FIGS. 2 and 3 are enlarged schematic side and front elevational views,respectively, of part of the apparatus of FIG. 1 showing an embodimentof a coating roller located outside of the dispersion supply tankproper;

FIG. 4 is a view corresponding to that of FIG. 2 showing a modificationof the embodiment thereof.

Referring now to the drawings and first, particularly, to FIG. Ithereof, there is shown a coating roller 18" which is rotatable so thatthe viscosity of a thixotropic dispersion being applied to a wire 2 isreduced. The coating roller 18" is located outside of a supply tank 6for thixotropic dispersion and is rotatably mounted in common with thesupply tank 6' on the shaft of a guide roller 8, as shown more clearlyin FIGS. 2 to 4, and described more fully hereinafter. The apparatus ofFIG. 1 includes a vertical arrangement of tubular furnaces traversed bya copper wire after the latter has been coated with thixotropicdispersion. A copper wire, having a diameter of 0.3 mm., for example, issupplied from a reel 1 and travels first through a cleaning bath 3 andsubsequently through an annealing device 4 having an internaltemperature of 500 C. and a reducing or inert atmosphere. The annealingdevice 4 serves to soften the copper material of the wire. The wire,thus cleaned and softened, then passes over succeeding guide rollers 5and 8 which direct it finally in a substantially vertical directionpassing through a space between opposed surfaces, such as on end plates,of the coating roller 6' and thence through a vertical arrangement I Iof furnaces which comprise three heating zones a, b and c ofrespectively different temperatures. The dispersion medium which issupplied to the coating roller 6, in a manner hereinafter more fullydescribed with regard to FIGS. 2 to 4, and applied by the roller 6' tothe copper wire 2, evaporates in the first heating zone a so that thewire 2, when entering the heating zone I), possesses a uniform andcentered or concentric covering of dry powder of thermoplastic syntheticmaterial such as polyethylene. This powder sinters together in theheating zone I) and fuses in the heating zone so as to form a coherentand smooth coating of the thermoplastic material.

The wire 2, when issuing from the vertical furnace II, is deflecteddownwardly by a guide roller 12 and pulled off by a pulling device 13 tobe wound upon a takeup drum 14.

For a pulling speed of m./min., there is required a length of about 60m. for the furnace 11 with the following temperature distribution:

zonea 2l0C.

zone b 240 C.

zone c 260 C.

Several wires are preferably simultaneously run through one and the samefurnace. In order to keep the number of wires as large as feasible, itis advisable to provide the vertical furnace 11 with a longitudinalheating chamber having a cross section of annular shape, and touniformly distribute the wires circumferentially over the annularheating space of the furnace.

While the wires to be insulated travel substantially vertically to thefurnace 11, an appreciable draft of air is caused to pass through thefurnace. In order to prevent oxidation of the thermoplastic materialsuch as polyethylene by the oxygen supplied in the air draft, thefurnace is preferably rinsed with inert gas in counterflow to the traveldirection of the wire. For example, hydrogen may be passed from abovethrough the furnace and along the wire.

In contrast to the embodiment shown and described in the aforementionedcopending application, the coating roller 18" of the instantapplication, due to the rotation of which the viscosity of thethixotropic dispersion is reduced, is mounted outside the supply tank 6'proper. A pump 24 is located within the supply tank 6 and by the aidthereof the thixotropic dispersion is supplied through a tube 25 to aside of the coating roller 18" which is located substantiallydiametrically opposite the side thereof along which the wire 2 passes ina vertical direction. At the location 26, a supply of thixotropicdispersion is formed which penetrates in part onto the spaced surfacesof the coating roller 18" between which the conductor wire 2 passes, thegreater portion of the thixotropic dispersion being held back in thesupply tank 6', however, by suitable wiper 27. The excess of thedispersion accordingly flows downwardly over a wiper 28 back into thesupply tank 6. The supply tank 6' is completely closed, except for theopening required due to the arrangement of the coating roller 18", thetube 25 and the wipers 27 and 28, so that evaporation of the dispersionmedium is reduced to a minimum. Furthermore, due to the aforedescribedcirculation of the dispersion medium, the formation of dead ends orstagnation pockets is avoided. The quantity of the dispersion suppliedto the coating roller 18" is determined both by the power of the pump 24and also by the adjustment of the wipers 27 and 28. The coat ing roller18" which is driven by a nonillustrated electrical motor, for example,rotates in a direction opposite to the direction in which the wire 2advances vertically. The thickness of the applied insulating coatingdepends approximately upon the rotary speed of the coating roller18",the value of which determines also the reduction of viscosity of thedispersion supplied to the wire 2 and depends also upon the spacing ofthe opposing surfaces and of the core of the coating roller 18" from thewire 2. In order to permit fine adjustment of thickness of the appliedcoating, the roller 18" is mounted so that it is adjustable in adirection perpendicular to the vertical direction in which the conductoris advanced.

The apparatus constructed in accordance with the invention of theinstant application has a further advantage over the embodimentdisclosed in the aforementioned copending application in that thereversing guide roller 8 is also located outside the dispersion.Consequently, if desired, the reversing guide 8 can be utilizedsimultaneously for imprinting, if the wire 2 which may have beenpreviously provided with a coating is to be suitably identified ormarked.

As aforementioned, the apparatus of my invention is suited particularlyfor coating a conductor with an insulating layer of polyethylene. Insuch a case it is recommended that the composition of the polyethylenedispersion of thixotropic structure be selected in such a manner as thatgiven in the aforementioned copending application. The followingcomposition of the dispersion, for example, has proven to beparticularly advantageous:

40 percent polyethylene powder (stabilized) having a median grain sizeof 20 p.

36.5 percent water 15 percent methyl alcohol I percentnonylphenolpolyglycol ether 2.5 percent hydrate cellulose 5 percentisopropyl alcohol As aforementioned, for practical realization ofapparatus according to the invention, it is recommended to permitseveral wires to pass through the apparatus simultaneously. In thismanner the capacity of the apparatus is greatly increased.

As a further feature of my invention, it can be provided that thecoating roller 18'', pivotable about a pivot point, be pressed bymechanical forces in a direction toward the conductor which is passed inthe vertical direction between the opposing surfaces of the coatingroller 18", whereby the spacing of the coating roller 18" from theconductors to be insulated is determined by an adjustable abutment ordetent. In this manner assurance is provided that the spacing betweenthe opposing surfaces of the coating roller 18" and the conductors thatare being insulated is also maintained during shaking and vibrationsoccurring in the course of the operation of the apparatus. For thispurpose, the coating roller 18" can be pressed by a spindle providedwith a worm thread, which acts upon a gear connected with the coatingroller 18", against the abutment or detent determining the spacingthereof from the conductors being insulated.

An example of such a construction of a coating roller located outside ofthe dispersion supply tank proper is shown schematically in FIGS. 2 and3. As can be seen in FIGS. 2 and- 3, the coating roller 18'', due to therotation of which the viscosity of thixotropic dispersion is reducedwhen applied to the wire 2, is located outside of the supply tank 6proper and is rotatably mounted in common with the latter on the shaftof the reversing roller 8. Additionally mounted on the shaft of thereversing roller 8 is a gear 29 in the teeth of which a worm thread of aspindle 30 meshes. By rotating the handwheel 31 the shaft of thereversing roller 8 and therewith the position of the coating roller 18can be twisted with respect to the vertically traversing wires 2. Thesize of this rotary motion is limited by the fact that a plate 32secured to the coating roller 18" abuts against a stop pin 33 at thelower end of the plate 32, as shown in FIG. 2, for example. Due to themechanical force which is exerted through the spindle 30 and the gear 29on the coating roller 18'', assurance is afforded that the relativeposition of the coating roller 18" and the vertically traversing wires 2are maintained even during the shaking and vibrations occurring in thecourse of operation of the apparatus. The amount of spacing between theopposing surfaces of the coating roller 18" and the wires 2 passingthrough the space therebetween is accordingly adjustable by the stop pin33 which can be suitably screwed into the and out of the thread holder34 thereof. It is also possible, however, to press the coating roller 18against the abutment or stop member, which determines the spacingbetween the coating roller and the conductors to be insulated, by meansof a lever provided with a weight. An embodiment of such apparatus isshown schematically in FIG. 4.

The embodiment of FIG. 4 differs from that of FIGS. 2 and 3 in that therotary motion of the coating roller 18", which is mounted on the shaftof the reversing roller 8, is effected by a lever 35 provided with aweight at the free end thereof. Due to the action of this lever 35, thelower end of the plate 32 connected to the coating roller 18" is pressedagainst the adjustable stop pin 33 in the same manner as in theembodiment shown in FIGS. 2 and 3.

With the aid of this lever 35 the adjustment of the spacing between theopposing surfaces of the coating roller 18" and the wires 2 which arebeing insulated and which are traversing therebetween is effected morerapidly than is possible with the spindle of the embodiment shown inFIGS. 2 and 3.

lclaim:

1. Apparatus for insulating thin copper wires and other thin electricconductors with a coating of a polyolefin, comprising a tank forcontaining an aqueous dispersion of thixotropic structure, a coatingroller mounted outside said tank and provided with a pair of spacedsurfaces between which an electric conductor is traversable in asubstantially vertical direction, said coating roller being rotatable ina direction opposite to the direction in which the electric conductor istraversable, said coating roller being pivotally mounted in a directionperpendicular to the substantially vertical direction in which theelectric conductor is traversable between said spaced surfaces of saidcoating roller for adjusting the distance between said coating rollerand the electric conductors being insulated, means for supplying thedispersion from said tank to said coating roller in an amount adequatefor coating the electric conductor therewith, mechanical force-applyingmeans for pressing the coating roller in a direction toward the electricconductors vertically travcrsable through the space between saidsurfaces of said coating roller, adjustable abutment means for limitingthe distance between said coating roller and the electric conductorsbeing insulated, and furnace means located upstream of said coatingroller and traversable by the dispersion coated electric conductor forheating the same to vaporize the dispersion medium and sinter theremaining pulverulent polyolefin on the conductor to form a homogeneouscoherent coating, and a gear connected to a plate on which said coatingroller is rotatably mounted, and a spindle formed with a worm threadmeshing with the teeth of said gear and coacting therewith for pressingsaid plate in direction against said abutment means.

